President Kwasniewski: Cleared on Wednesday

President Aleksander Kwasniewski, an ex-communist whom many predict will win re-election in the October poll, was co-accused with Mr Walesa, but acquitted on Thursday.

Although Mr Walesa's is now free to run for president, his chances of victory are believed to be slim.

A recent poll gave him a meagre 3% support, but as a result of Friday's ruling, his place in history as the father of modern Polish democracy appears to be safe.

Debate

A BBC correspondent says the case has sparked a debate over the nature of democracy in Poland and the role of Lech Walesa.

Lech Walesa

1980: Becomes leader of Solidarity 1981: Arrested in anti-democracy crackdown 1982: Released, Polish martial law eased 1983: Awarded Nobel peace prize 1984: Solidarity legalised 1990: Elected president of Poland 1995: Defeated in presidential election 2000: Cleared of charges of working with Communist state police

Awarded a Nobel laureate prize, Mr Walesa's success as Solidarity leader was not matched by his unspectacular stint as Polish president, which ended with his defeat at polls in 1995.

However, the affair has raised questions of how strong democracy actually is in Poland if candidates for political office can be excluded on the basis of what they did during the past.

Critics have also attacked the use of old police documents as evidence because the secret services often used to deliberately work to discredit opponents of the communist regime.